Diagnostic and prognostic utility of pleural fluid neutrophil-to-lymphocyte and monocyte-to-lymphocyte ratios in exudative pleural effusion

Abstract Background Exudative pleural effusion (EPE) remains a diagnostic and therapeutic challenge. Inflammatory biomarkers, such as the neutrophil-to-lymphocyte ratio (NLR) and monocyte-to-lymphocyte ratio (MLR), have been proposed as non-invasive, cost-effective tools for diagnosis and prognosis. This study aimed to evaluate the diagnostic accuracy and prognostic significance of pleural fluid NLR and MLR in EPE. Methods This prospective cohort study included 60 patients with EPE at Alexandria Main University Hospital. Pleural fluid was analyzed for cell differentials, including neutrophils, monocytes, and lymphocytes. NLR and MLR were calculated. Diagnostic accuracy in differentiating malignant from non-malignant effusions and prognostic outcomes, including ICU admission, 30-day mortality, and recurrence, were evaluated. Results NLR and MLR were significantly lower in malignant pleural effusions (NLR: 1.21 ± 0.68; MLR: 0.19 ± 0.09) compared to benign effusions (NLR: 2.65 ± 1.24; MLR: 0.34 ± 0.13), with p < 0.001. A high NLR was significantly associated with ICU admission (30% vs. 10%, p = 0.03), higher 30-day mortality (20% vs. 3.3%, p = 0.04), and recurrence (36.7% vs. 13.3%, p = 0.02). Conclusion Pleural fluid neutrophil-to-lymphocyte and monocyte-to-lymphocyte ratios are practical, inexpensive, and non-invasive markers for differentiating between malignant and benign exudative pleural effusions. Moreover, high NLR values correlate with adverse clinical outcomes, making it a potential tool for prognostication. Incorporating these markers into routine pleural fluid analysis could enhance diagnostic accuracy and inform management strategies, especially in settings with limited resources.